This invention relates to a vibration damper which includes a damping mass supported in an at least partially closed housing by means of at least two spring elements.
Vibration dampers for reducing the vibrational energy in power hammers or drills are known. Such a device is described, for example, in British Pat. No. 1,421,032. According to this patent, a damping element (damping mass) is supported by means of spring elements at the inner wall of a bore provided, for example, in drilling rods or in a cavity of a housing to be attached to a machine whose vibrations are to be damped. The damping element is supported by the spring elements in such a manner that the spring elements are in contact with the damping element as well as with the oppositely located end walls (impact faces) of the bore or cavity. Further, a mechanism is provided for axially adjustably compressing the spring elements in order to vary their stiffness. At least one of the end walls or the end face of the spring element is--as viewed in an uncompressed state--of conical shape and defines a wedge-shaped gap when no compression force is applied. By means of this arrangement both the damping force and the spring force may be adjusted. While, from the theoretical point of view, the efficiency of such an arrangement is undisputed, difficulties are involved with its technical realization, because in using a rubber member for the spring elements there is generated a friction between the associated impact face of the bore and the surface of the spring element. This occurrence leads to a wear of the spring element. The friction could be reduced by lubrication which, however, is not feasible in case of certain elastomers. Further, polybutadiene would be otherwise an appropriate material as concerns the dynamic deformation behavior; such materials, however, are not oil-resistant.
U.S. Pat. No. 3,968,843 discloses an improvement with respect to the arrangement described in the above British patent. An elastic damping member is arranged between a vibrating tool and a handle and is provided with throughgoing air supply channels. Further, an oil-resistant, one-piece elastic lining is provided on the walls of the air supply channels. This arrangement prevents oil carried with the compressed air from contacting the rubber material of the damping member. Further, the lining is used on either side of the damping member for sealing the air supply channels. Such an arrangement may yield advantageous results in certain instances, particularly where the damping member or, as the case may be, the spring element is secured at both sides and no relative displacements whatever are allowed between the damping mass and the spring element on the one hand, and between the spring element and the handle on the other hand, as it should be the case between the tool and its handle.